1. Field of the Invention
The present invention relates to a semiconductor material having an irregular or disordered structure and, more particularly, to an improvement in an optical function and performance of a semiconductor material.
2. Description of the Related Art
As a semiconductor material for a light-emitting device, single crystal gallium arsenide (GaAs) or an amorphous silicon (Si) semiconductor has been conventionally used. Single crystal GaAs has the direct band structure and is suitable as a light-emitting material. Since, however, an energy band width of single crystal GaAs is .epsilon..sub.g =1.43 eV, its light-emission wavelength .lambda. is 0.867 .mu.m, i.e., an infrared light. An amorphous Si semiconductor has a high light-emission intensity obtained by recombination through its localized level and has properties suitable as a material for a light-emitting device. Amorphous Si, however, cannot be epitaxially grown. Therefore, it is difficult to fabricate a device which requires epitaxial growth on the amorphous silicon.
Although a single crystal silicon (Si) semiconductor material can be epitaxially grown, it has the indirect band structure. Therefore, single crystal Si is not suitable as a material for a light-emitting device.
AlP and GaP have energy band widths of .epsilon..sub.g =2.43 eV (.lambda.=0.510 .mu.m) and .epsilon..sub.g =2.25 eV (.lambda.=0.551 .mu.m), respectively, and emission light colors of green and yellowish green, respectively. Therefore, both the materials can emit visible light. Since, however, both the materials have the indirect band structure, their light-emission efficiencies are very low.
As described above, the conventional semiconductor materials for a light-emitting device have specific problems, respectively.